Catheters (including both standard catheters and so-called vascular sheaths) are used in a wide variety of medical procedures. For example, some catheters are used to reach selected sites within the human vasculature so that a drug can be delivered to a specific site. Alternatively, a second medical device, such as a stent or septal defect occlusion device, may be delivered to the desired location through the catheter.
Other catheters include the capability to perform additional functions. For example, balloon catheters can be inflated to perform angioplasty or temporarily or permanently occlude a vessel. Other catheters include optical systems to permit a physician to visualize a remote site within the body, such as in endoscopy.
One of the primary difficulties in using a catheter is properly positioning the catheter within the desired body channel or cavity. In positioning a catheter within a patient's vasculature, for example, the physician will typically guide a thin, relatively steerable guidewire into position adjacent the desired location and then urge the catheter over the guidewire. The catheter will ostensibly track the guidewire and can be placed in the desired location in that manner. If the guidewire is removed from the catheter, though, it is not uncommon for the distal tip of the catheter to become unseated from a desired location. This is believed to be due to an inherent restoring force of the catheter walls--upon removal of the constraint of the guidewire, the catheter will tend to return toward its natural, unstressed state and this spring force can pull the tip of the catheter out of a particular branch of a vessel.
Some catheters are guided into place without the use of guidewires. So long as the catheter has sufficient "pushability," i.e., can be urged distally from a proximal location without buckling or kinking, this can reduce the number of steps in deploying a catheter to a single procedure. Unfortunately, such guide catheters tend to be more difficult to steer into position and their stiffness necessarily limits their deployment in more tortuous vessels.
Both to help seat catheters in the desired location and to help physicians steer guide catheters without the use of a guidewire, a number of physicians have proposed shaping the catheter tip in a particular fashion. This does make it easier to deploy the catheter in one specific type of procedure. Unfortunately, each specific type of procedure will commonly have one or two optimized catheter designs which have less utility in other procedures. Accordingly, there has been a very rapid increase in the number of different catheter designs that hospitals must stock to provide their physicians with a suitable array of state-of-the-art catheters. The problem is made even more acute by the fact that differently sized patients will have differently sized vasculatures. Hence, even for a single catheter design for use in a single type of procedure, one may have to carry several different sizes to accommodate children, small adults and large adults.
One other disadvantage of pre-formed, off-the-shelf catheters is that they do not allow the physician to take into account any peculiarities of a patient's vascular system. Instead, physicians are expected to do the best they can with the off-the-shelf catheters. Some physicians choose to take a different approach and customize the catheter they intend to use in a procedure to meet the anticipated needs. Most catheters are formed of a thermoplastic material and can be reshaped to some extent when heated. A physician may, for example, heat a length of the catheter until it becomes maleable, then reshape the heated length. When it cools down, the catheter will retain at least some of the modified shape imposed while it was heated.
Such crude reconstruction after the fact, however, has its own problems. First, it is obviously relatively time-consuming and requires the physician to have more equipment in the operating theater. In addition, if the physician discovers during a procedure that the patient's vasculature is different from what was anticipated, the physician would either have to utilize a pre-formed catheter or would have to suspend the procedure while he or she shaped an appropriate catheter. Another problem with such manual reshaping is that it can, in some circumstances, compromise the lumen of the catheter. When a catheter is bent, particularly through more acute angles, the lumen will have a tendency to at least "ovalize," i.e., the generally circular lumen may flatten out to some extent, or even kink and effectively seal at a bend. Where high flow rates of fluid are necessary or when a medical device must be passed through the catheter, such ovalization or kinking can make the catheter virtually useless.
Some catheters and endoscopes can be remotely steered. For example, U.S. Pat. No. 5,325,845 (issued to Adair in 1994, the teachings of which are incorporated herein by reference) suggests a steerable sheath for use in connection with optical catheters. The proximal end of the catheter is provided with a pair of steering knobs which are connected to wires that run along the length of the catheter. Each knob controls a pair of diametrically opposed wires and all four of the wires are attached to the distal tip of the catheter. By appropriate manipulation of either of the control knobs, one can ostensibly control the position of the distal tip of the catheter. By such remote manipulation, the reference claims a physician can move the optical catheter into position to view the desired site.
Others have proposed similar uses of cables in endoscopic procedures. For example, U.S. Pat. No. 4,700,693 (issued to Lia et al., in 1987, the teachings of which are incorporated herein by reference) suggests a design which utilizes steering cables and a number of washers. The steering cables can be remotely manipulated to guide the endoscope through a desired curve.